1972 Runs Rough - Possibly Rebuild or Replace Carburetor?

[John A.]

Every once in a while it will run perfectly, but most of the time it has a bobble when driving/pressing the accelerator (not a bog that works itself out, but a continual bobble, even at high speeds like something is blocking the jets...and restricting fuel flow). When this occurs, it is also difficult to keep it at idle when stopped unless I keep my foot on the gas pedal to maintain a higher idle. Sometimes it will idle on its own around 650-700 rpm, but many times it dips down below 500 rpm and would stall unless I kept my food on the gas. The choke on cold start works fine (idles fast until it warms up).

I changed the spark plugs and fuel filter about 3,000 miles ago, sprayed the carburetor with cleaner on several occasions, and used various additives over the past year in the gas to see if that would help. Still the problem persists and the plug tips now are covered with black soot from what I assume is from runing rich/fuel loading. I am not sure if I should try and clean/rebuild the carburetor, send it out for a professional rebuild, or buy a new one (and obviously keep the original in a box). I am looking for something that will be reliable so my wife can just get in and drive/enjoy the car.

Someone recently told me that they sent their Quadrajet out for a rebuild on two occasions and it still never ran perfectly, so they switched to a 600 cfm Holley and they have been happy ever since.

I was thinking about buying Ecklers universal Holley 600 cfm carburetor with vacuum secondaries and electric choke that is listed as a replacement (see link), but wanted to see if any of you had thoughts on the issue or potential replacement carburetor to include if anyone has used the below Holley. I saw a thread that someone has had success with the Holley 6210 and mechanical choke, but I am not sure that carburetor is the right one for me. If new is the way to go then I would be looking for a carburetor that mounts to the stock manifold.

http://www.ecklerscorvette.com/corvette-carburetor-600cfm-holley-universal.html#

Thanks,
John

[Patrick H.]

Re: 1972 Runs Rough - Possibly Rebuild or Replace Carburetor?

John,

With a few 72 Corvettes in the garage I can tell you that there is absolutely no reason you can't get it to run well with the current carb. It may need work or it may be a different issue, but Quadrajets can work very well.

Where in Maryland do you live?
If you are anywhere near Gaithersburg I'd highly recommend stopping by Tony's:

http://www.tonyscorvetteshop.com/index.aspx

He can diagnose it better in person than any of us can from afar.

Patrick

[Edward J.]

Re: 1972 Runs Rough - Possibly Rebuild or Replace Carburetor?

John, is the choke butterfly staying closed or maybe not opening all the way as the engine warms and causing the car to load up the spark plugs? if the butterfly is not opening all the way the will enrich the mixture and foul out the plugs in quick order. alot of times the linkage for fast idle and choke need cleaning and lubrication to the choke working properly. they get sticky or gummy after the years.

[Michael W.]

Re: 1972 Runs Rough - Possibly Rebuild or Replace Carburetor?

90% of what you describe could be caused by a sticking float or leaking valve and seat, a simple fix. Do not downgrade your car with a Holley or Edelbrock antique.

[John A.]

Re: 1972 Runs Rough - Possibly Rebuild or Replace Carburetor?

Thanks to all so far for the responses. I checked the front throttle plate and it does open fully upon warm up, but I lubricated some of the linkage points as per Ed. I noticed some very minor weapage (maybe just permeating through the gasket) at some of the gaskets points (like between a portion of the throttle body and float bowl assemblies). No fuel pouring out just some localized dampness and gunk buildup on the face of the carburetor along some of the gasket areas. Maybe a carburetor rebuild kit like what Eckler's sells would do the trick? http://www.ecklerscorvette.com/corve...lock-1972.html

[Patrick H.]

Re: 1972 Runs Rough - Possibly Rebuild or Replace Carburetor?

Thanks to all so far for the responses. I checked the front throttle plate and it does open fully upon warm up, but I lubricated some of the linkage points as per Ed. I noticed some very minor weapage (maybe just permeating through the gasket) at some of the gaskets points (like between a portion of the throttle body and float bowl assemblies). No fuel pouring out just some localized dampness and gunk buildup on the face of the carburetor along some of the gasket areas. Maybe a carburetor rebuild kit like what Eckler's sells would do the trick? http://www.ecklerscorvette.com/corve...lock-1972.html

Probably not.
You need to diagnose the problem, not throw parts at the car.

Apparently you don't live close enough to Tony's to pay a visit?

[Roy V.]

Re: 1972 Runs Rough - Possibly Rebuild or Replace Carburetor?

run a can of Seafoam through it, pour some directly into the carb.
Hey....., what could it hurt.
Regards
Roy

[John A.]

Re: 1972 Runs Rough - Possibly Rebuild or Replace Carburetor?

Thanks and I called and left a message for Tony (he could not take it today)--so hopefully I can swing by there in the next week or so.

[Joe L.]

Re: 1972 Runs Rough - Possibly Rebuild or Replace Carburetor?

Thanks and I called and left a message for Tony (he could not take it today)--so hopefully I can swing by there in the next week or so.

John-----

My guess is that you have a "heavy" carburetor float. The symptoms you describe are entirely consistent with that condition. QuadraJets use a nitrophyl plastic float. After long service the coating on the float wears away and the porous nitrophyl material absorbs gas and becomes "heavy". The solution is to replace the float. At the same time, I would rebuild the carburetor with a new kit. If this is an original carb and has never been "messed with" by some klutz, you should be able to rebuild it and have it run perfectly. Often times, problems with rebuilt QuadraJets stem from commercially rebuilt units using cores of "unknown history" (i.e. carburetors that have been "messed with" by some klutz and rendered "ruined forever".

By the way, the GM/Delco float for your application is discontinued. However, you can obtain an exact replacement as manufactured by Standard Auto Products of their number FL1. There are also brass replacements for the nitrophyl floats available on the market. These would seem to solve the "heavy" float problem forever. Nevertheless, I do not recommend their use.

[Patrick H.]

Re: 1972 Runs Rough - Possibly Rebuild or Replace Carburetor?

John-----

My guess is that you have a "heavy" carburetor float. The symptoms you describe are entirely consistent with that condition. QuadraJets use a nitrophyl plastic float. After long service the coating on the float wears away and the porous nitrophyl material absorbs gas and becomes "heavy". The solution is to replace the float. At the same time, I would rebuild the carburetor with a new kit. If this is an original carb and has never been "messed with" by some klutz, you should be able to rebuild it and have it run perfectly. Often times, problems with rebuilt QuadraJets stem from commercially rebuilt units using cores of "unknown history" (i.e. carburetors that have been "messed with" by some klutz and rendered "ruined forever".

By the way, the GM/Delco float for your application is discontinued. However, you can obtain an exact replacement as manufactured by Standard Auto Products of their number FL1. There are also brass replacements for the nitrophyl floats available on the market. These would seem to solve the "heavy" float problem forever. Nevertheless, I do not recommend their use.

In addition, the vast majority of carburetor kits available from parts stores, catalog vendors, etc are absolute junk.

The best ones I know of are Cliff's:

http://www.cliffshighperformance.com/carbkits.html

If anyone else knows of a quality kit feel free to chime in, but they are few and far between.

Patrick

[Jim T.]

Re: 1972 Runs Rough - Possibly Rebuild or Replace Carburetor?

So I downgraded my 1968 and 1970 original owner Corvettes in 1974 when I installed Holley 6210 650 spreadbore double pumpers on my Corvette's original intakes. Even after all these years, my Holley equipped Corvettes start up quicker and run better than the original QJets I removed. The chokes work from the same coiled spring mounted on the original intakes that the QJets used. A lot of Corvettes left the factory with Holley carburetors. With my last purchased Holley carburetor rebuild kit, it was nice to be able to still purchase good parts.

[Michael W.]

Re: 1972 Runs Rough - Possibly Rebuild or Replace Carburetor?

In addition, the vast majority of carburetor kits available from parts stores, catalog vendors, etc are absolute junk.

The best ones I know of are Cliff's:

http://www.cliffshighperformance.com/carbkits.html

If anyone else knows of a quality kit feel free to chime in, but they are few and far between.

Patrick

Good advice Patrick. There is also some discussion about accelerator pumps that are NOT compatible with E10 still being flogged. I think Lars Grimsrund has the skinny on that.

[Paul H.]

Re: 1972 Runs Rough - Possibly Rebuild or Replace Carburetor?

So I downgraded my 1968 and 1970 original owner Corvettes in 1974 when I installed Holley 6210 650 spreadbore double pumpers on my Corvette's original intakes. Even after all these years, my Holley equipped Corvettes start up quicker and run better than the original QJets I removed. The chokes work from the same coiled spring mounted on the original intakes that the QJets used. A lot of Corvettes left the factory with Holley carburetors. With my last purchased Holley carburetor rebuild kit, it was nice to be able to still purchase good parts.

I bolted on the Holley 6210 Spreadbore on my 68 427/390 several years ago. Best carb I ever bought. Great throttle response throughout the RPM range. Much quicker starts. Smooth idle. I know some like the QJ. I do not. Count me in as another that "downgraded".

Lars over on the Corvette Forum is extremely competent if you want to keep the QJ. Mail the carb to him. Turnaround is often less than a week.

[Francis F.]

Re: 1972 Runs Rough - Possibly Rebuild or Replace Carburetor?

Yes John I had similar problem's with my "60" then again on the "66" sb with a Holley.I had a friend over and he pulled the air cleaner,and found the rear float STUCK and dumping large amounts of gas right into the intake.
Pulled the float and thus the engine returned to a smooth running machine.hope this works for you also.
Francis

[John A.]

Re: 1972 Runs Rough - Possibly Rebuild or Replace Carburetor?

Thanks Paul...

John